1. Field of the Invention
Scientists are currently seeking effective alternatives to conventional chemical methods for crop pest management. One promising approach has been the application of biological control agents. The discovery and development of biological systems which are detrimental to targeted pests but harmless to the environment have thus assumed a high priority. This invention relates to baculoviruses genetically engineered to produce a peptide hormone which, when present in sufficient amounts, results in weight and water loss and the eventual death of these insects. Such peptides have been isolated from the corn earworm Helicoverpa zea and related species, and have been identified as helicokinins.
2. Description of the Relevant Art
Insect infestation is a major cause of crop loss throughout the United States. The corn earworm Helicoverpa zea (H. zea) causes an estimated $1.2 billion in crop damage each year and, together with Helicoverpa armigera (H. armigera) and a related species, Heliothis virescens (H. virescens), constitutes the most important group of crop pests throughout the world. H. zea and H. armigera together cause crop damage resulting in losses worth over $5 billion annually.
Chemical pesticides have conventionally been relied upon to control insect pest populations. Environmental and consumer safety concerns, however, have led to the deregistration of many pesticides and a reluctance to use others on agricultural products which are ultimately intended for human or animal consumption. In addition, the increasing resistance of insects to chemical pesticides has resulted in a reduction in their susceptibility to the insecticidal activity of the chemicals. Scientists have therefore pursued the development of biological agents as an alternative for effective control.
Attempts have been made to exploit the natural sex attractants of insects in order to disrupt reproductive behavior. Sekul et al. [J. Econ. Entomology. 1975. vol. 68(5), pp. 603-604], for example, identified a compound, Z-11-hexadecenal, which is produced and released by the adult female of H. zea and referred to as a sex attractant inhibitor. Sparks et al. (Southern Cooperative Series Bulletin. 1988. pp. 50-65) discussed Heliothis pheromones and their potential use as biocontrol agents by mating disruption. Raina et al. (U.S. Pat. No. 5,032,567, 1991) disclosed a neuropeptide referred to as Hez-PBAN. The peptide was isolated from H. zea adults and activated pheromone biosynthesis in female moths as well as melanization in the larvae. Pheromone production at the wrong time of day can prove hazardous to females, and larval melanization is often fatal. Kingan et al. (U.S. Pat. No. 5,344,821, 1994) disclosed a pheromonostatic polypeptide obtained from male H. zea which, upon injection into the female, stops pheromone production and renders the female unattractive to male insects.
Another approach involved the use of baculoviruses (Wood, H. A. 1996. In Molecular Biology of the Biological Control of Pests and Diseases of Plants. Gunasekaran and Weber, ed., CRC Press, Inc., Boca Raton, Fla., pp. 91-104, herein incorporated by reference). Naturally-occurring baculoviruses are known insect pathogens capable of effecting reduction in insect populations. This capability led to the expectation that the viruses could be utilized safely and effectively in biological control applications. In addition, recombinant baculoviruses expressing various pesticidal genes have been produced.
While these approaches have shown potential for controlling corn earworm populations, consistent success has proven elusive and difficult to achieve for various reasons: lack of an effective carrier or vector in the case of mating disruption, the high cost of production and low activity in the case of naturally-occurring baculoviruses and the lack of culture systems necessary for propagating recombinant baculoviruses. The need for a reliable and consistent means for controlling H. zea populations in the field thus remains an important goal.